The present invention generally relates to data control systems, and more particularly to a data control system for a virtual machine system.
In order to meet the demands to increase the scale and speed of computer systems, there are proposals to realize a high-speed large-quantity data transfer within the system and between the systems using an external storage. There are similar demands on the virtual machine system. Hence, there are proposals to assign an external storage for each virtual machine so as to realize a data transfer within the virtual machine and between the virtual machines using the external storage.
However, when the data transfer quantity is large, the data transfer process may be concentrate on a specific virtual machine and cause problems.
In a native environment other than the virtual machine system, a number of paths between the external storage and the main storage generally does not become smaller than the number of systems. For this reason, a path used for the data transfer between the main storage and the external storage in one system will not be used by another system, and a transfer request will not have to wait. In other words, a situation where the transfer request must wait because the path used for the data transfer between the main storage and the external storage of the system is being used by another system will not occur.
However, in the virtual machine system, the number of paths between the main storage and the external storage may be smaller than the number of virtual systems. Consequently, when a virtual machine transfers a large quantity of data to the external storage, this virtual machine exclusively uses the path between the main storage and the external storage for a long time. As a result, the transfer requests of other virtual machines which cannot use the path must wait until the path becomes free, and the actual data transfers are greatly delayed.
Accordingly, when an operating system which operates on the virtual machine carries out a data transfer between the main storage and the external storage during a process such as a paging process which affects the entire performance of the operating system, the performance of the operating system is greatly affected and there is a problem in that the performance greatly differs for each virtual machine.